If and when physicists are able to pin down the metal content of the sun, that number could upend much of what we thought we knew about the evolution and life span of stars.
Twenty years ago, astronomers thought they had the sun sorted. Direct and indirect ways of inferring its metallicity both gauged the sun as approximately 1.8 percent metal — a happy convergence that led them to believe they understood not only the length of their solar yardstick but also how the sun works. However, throughout the 2000s, increasingly precise spectroscopic measurements of sunlight — a direct probe of the sun’s composition, since each element creates telltale absorption lines in the spectrum — indicated a far lower metallicity of just 1.3 percent. Meanwhile, helioseismology, the competing, indirect approach for inferring metallicity based on the way sound waves of different frequencies propagate through the sun’s interior, still said 1.8 percent.